1. Field of the Invention
This invention relates generally to devices for transmitting both electric and mechanical power across an interface and more particularly to an electromechanical type rotary joint including gear type coupling elements.
2. Description of the Prior Art
Means for coupling electrical current or power across an interface typically includes such apparatus as electrical cables and/or transformers. Where transmission of current and power are further required across a movable, i.e. rotatable mechanical interface, slip rings or roll rings have been typically employed.
Slip rings are devices which are well known and have been widely utilized in space and industrial applications. However, it is well known that they do not in principle have smooth electrical transfer characteristics because since they are based on a sliding, friction process, they tend to hop and skip slightly as the members move with respect to one another. This adversely affects the signal to noise ratio of the system. It also adversely affects wear and reliability. Furthermore, for high speed rotating members where many rotations are involved, particularly in a vacuum such as in outer space, the problems with slip rings become greatly exacerbated.
With respect to roll rings, they cannot be fixedly located between two rotating members separated by a gap type of interface, as they tend to wander as the joint members move relative to one another. Consequently, if one or more roll ring is used, they can easily bump into one another, which in turn causes spikes in the conducting current. As a result, either separating techniques must be used, which in the past have proven much more involved than they are worth, or only a single rolling disk is used in any one orbit. Additionally, roll rings can only carry current. They cannot be used to additionally act as a mechanical power transmission system.
In robotic applications where rotary joints are located, electrical power transmission typically use electrical cables and transformers. Cables, however, are much too bulky and heavy and do not permit continuous rotations. Also, they are subject to being snagged and tearing. In certain circumstances, it can degrade as a result of continuous flexing. In every instance, particularly at a robot wrist, the cable must be looped around the robot structure in such a way that it can permit the wrist to turn .+-.180.degree.. Such arrangements are typically awkward, consume large amounts of space and are subject to snagging. With respect to transformers, such apparatus typically requires higher frequency AC power. Moreover, they are generally heavy and bulky. Furthermore, the coupling coils must be placed in close proximity to each other and this means extra precision in fabrication. Also there is generally significant electrical losses in the air gaps between the coils.
With respect to mechanical power transmission across robotic interfaces, state of the art anti-backlash gears have had wide utilization but do not include electrical transmission. Anti-backlash gears are normally comprised of pairs of counter rotating gears which are driven opposite each other and being intercoupled by a spring. This increases the size more than is desired and tends to be more complex and expensive than is necessary.